The present invention relates to the preparation of anisaldehyde, and more particularly to the preparation of anisaldehyde by the oxidation of p-methoxytoluene in the vapor phase in the presence of a novel catalyst.
It is known from Chemical Abstracts, Vol. 66, 2847u(1967), Chemical Abstracts, Vol. 74, 125060d(1971) and U.S.S.R. Pat. No. 360,844 that anisaldehyde is prepared by oxidizing p-methoxytoluene in the liquid phase in the presence of a catalyst. However, it has never been known that p-methoxytoluene can be converted to anisaldehyde by oxidation in the vapor phase.
It is also known that a methyl group attached to an aromatic ring is converted to an aldehyde by oxidation in the vapor phase. For instance, it is known that an aromatic compound such as toluene ro xylene is converted to the corresponding aldehyde by oxidation in the vapor phase with a catalyst containing molybdenum as a main component or a catalyst consisting of vanadium oxide and phosphorus oxide. The present inventors have attempted to oxidize p-methoxytoluene in the vapor phase by employing a catalyst containing molybdenum as a main component or a catalyst consisting of vanadium oxide and phosphorus oxide. However, in case of the catalyst containing molybdenum, the catalyst does not show any catalytic activity with respect to p-methoxytoluene. Also, in case of the catalyst consisting of vanadium oxide and phosphorus oxide, p-methoxytoluene is oxidized to carbon dioxide and water in one step and anisaldehyde is not produced.